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The polynomial hierarchy plays a central role in classical complexity theory. Here, we define a quantum generalization of the polynomial hierarchy, and initiate its study. We show that not only are there natural complete problems for the…

Quantum Physics · Physics 2016-10-25 Sevag Gharibian , Julia Kempe

A key issue of current quantum advantage experiments is that their verification requires a full classical simulation of the ideal computation. This limits the regime in which the experiments can be verified to precisely the regime in which…

Quantum Physics · Physics 2025-10-08 Abhinav Deshpande , Bill Fefferman , Soumik Ghosh , Michael Gullans , Dominik Hangleiter

Quantum advantage is notoriously hard to find and even harder to prove. For example the class of functions computable with classical physics actually exactly coincides with the class computable quantum-mechanically. It is strongly believed,…

Quantum Physics · Physics 2015-10-07 Howard Dale , David Jennings , Terry Rudolph

Quantifying the complexity of quantum states is a longstanding key problem in various subfields of science, ranging from quantum computing to the black-hole theory. The lower bound on quantum pure state complexity has been shown to grow…

Quantum Physics · Physics 2025-05-22 Yusen Wu , Bujiao Wu , Yanqi Song , Xiao Yuan , Jingbo B. Wang

A major obstacle towards realizing a practical quantum computer is the noise that arises due to system-environment interactions. While it is very well known that quantum error correction (QEC) provides a way to protect against errors that…

Quantum Physics · Physics 2023-02-24 Akshaya Jayashankar

The number of qubits used by a quantum algorithm will be a crucial computational resource for the foreseeable future. We show how to obtain the classical query complexity for continuous problems. We then establish a simple formula for a…

Quantum Physics · Physics 2007-05-23 A. Papageorgiou , J. F. Traub

The quantum Fourier transform (QFT) is a crucial subroutine in many quantum algorithms. In this paper, we study the exact lower bound problem of CNOT gate complexity for fault-tolerant QFT. First, we consider approximating the ancilla-free…

Quantum Physics · Physics 2024-09-05 Qiqing Xia , Huiqin Xie , Li Yang

Quantum computers, with parallel computing and entanglement effects, excel in cryptography analysis and big data processing. However, they are not fully developed yet, and their performance needs further evaluation. Traditional computer…

Quantum Physics · Physics 2024-09-11 Zili Chen

Quantum neural networks (QNNs) and quantum kernels stand as prominent figures in the realm of quantum machine learning, poised to leverage the nascent capabilities of near-term quantum computers to surmount classical machine learning…

Quantum Physics · Physics 2023-12-14 Yiming Huang , Huiyuan Wang , Yuxuan Du , Xiao Yuan

In the last decade, public and industrial research funding has moved quantum computing from the early promises of Shor's algorithm through experiments to the era of noisy intermediate scale quantum devices (NISQ) for solving real-world…

Quantum Physics · Physics 2023-04-05 Rhonda Au-Yeung , Nicholas Chancellor , Pascal Halffmann

Quantum computers offer the potential to simulate nuclear processes that are classically intractable. With the goal of understanding the necessary quantum resources to realize this potential, we employ state-of-the-art…

Protein folding processes are a vital aspect of molecular biology that is hard to simulate with conventional computers. Quantum algorithms have been proven superior for certain problems and may help tackle this complex life science…

Quantum Physics · Physics 2024-09-11 Hanna Linn , Isak Brundin , Laura García-Álvarez , Göran Johansson

In the last couple of decades, the world has seen several stunning instances of quantum algorithms that provably outperform the best classical algorithms. For most problems, however, it is currently unknown whether quantum algorithms can…

We observe that fault-tolerant quantum computers have an optimal advantage over classical computers in approximating solutions to many NP optimization problems. This observation however gives nothing in practice.

Quantum Physics · Physics 2022-12-27 Mario Szegedy

We introduce a new model for studying quantum data structure problems -- the "quantum cell probe model". We prove a lower bound for the static predecessor problem in the address-only version of this model where we allow quantum parallelism…

Quantum Physics · Physics 2007-05-23 Pranab Sen , S. Venkatesh

Quantum algorithms are getting extremely popular due to their potential to significantly outperform classical algorithms. Yet, applying quantum algorithms to optimization problems meets challenges related to the efficiency of quantum…

Quantum computing is gaining increased attention as a potential way to speed up simulations of physical systems, and it is also of interest to apply it to simulations of classical plasmas. However, quantum information science is…

Plasma Physics · Physics 2024-06-19 I. Y. Dodin , E. A. Startsev

Particle physics underpins our understanding of the world at a fundamental level by describing the interplay of matter and forces through gauge theories. Yet, despite their unmatched success, the intrinsic quantum mechanical nature of gauge…

Finite-sum optimization has wide applications in machine learning, covering important problems such as support vector machines, regression, etc. In this paper, we initiate the study of solving finite-sum optimization problems by quantum…

Quantum Physics · Physics 2024-06-06 Yexin Zhang , Chenyi Zhang , Cong Fang , Liwei Wang , Tongyang Li

The quantum computer is supposed to process information by applying unitary transformations to the complex amplitudes defining the state of N qubits. A useful machine needing N=1000 or more, the number of continuous parameters describing…

Quantum Physics · Physics 2014-09-23 M. I. Dyakonov